The go kart:
Objective
My goal was to construct a go-kart entirely from wood, a material not typically used for this purpose. This unconventional choice allowed me to explore principles of materials engineering.
Planning
Design Sketch: I began by drawing a basic outline of the go-kart to conceptualize its structure.
Dimensioning: To determine exact measurements, I outlined the go-kart dimensions directly on my floor using tape, ensuring a clear and accurate layout.
I decided on specific dimensions (5 feet long by 3 feet wide) for the go-kart.
After purchasing the necessary materials, I had the wooden pieces cut to size.
The rear axle, essential for connecting the wheels and enabling their rotation, was my first focus. Due to initial budget constraints, I selected a cost-effective axle. However, this came with challenges:
- T8F chains were unavailable.
- The clutch used on standard go-kart engines was incompatible with T8F chains
Clutch Analogy:
Imagine you're on a merry-go-round. As it spins faster, you feel pushed outward due to centrifugal force. Similarly, in a centrifugal clutch: As the engine spins faster, centrifugal force pushes brake shoes outward. These shoes grip the clutch housing, transferring power from the engine to the wheels.
Proposed Solution for the Sprocket Issue
My first idea was to purchase a sprocket that could attach to the T8F sprocket, combining its teeth with a 420 sprocket to achieve compatibility with the clutch and chain system. (I just bolted the two sprockets together)
Steering System
To address steering challenges, I first studied how a steering system works:
I designed and 3D-printed a piece to stabilize the entire steering assembly and prevent unnecessary movement.
Using the rack-and-pinion mechanism, I developed a method to translate its movement into wheel turns for go karts:
When one side of the system was pulled during a turn, it caused the corresponding wheel to turn inward, directing the go-kart appropriately.
Material Challenges
Because the plastic components I initially 3D-printed snapped under weight, I purchased the same parts made out of steel for added durability and functionality. I then purchased a giant piece of steel square tube and had it cut to size. I then had this piece of tubing weldded to the spindle mechanism.
Brakes
Every vehicle needs brakes—that's obvious. However, when it came to go-karts, the options were limited. I initially purchased hydraulic brakes, but over time they proved insufficient. So, I switched to mechanical brakes. Both systems operate similarly in that they use two steel plates to clamp onto a brake disc. The key difference is that hydraulic brakes use fluid pressure to engage the pads, while mechanical brakes use a direct mechanical linkage—one pad remains stationary as the other is pushed against it.
Gas Pedal and Kill Switch Wiring
The gas pedal connects via a steel cable linkage directly to the throttle arm on the 212cc engine. When pressed, the cable pulls the throttle arm, opening the carburetor butterfly valve to increase fuel flow and engine RPM. The kill switch wiring runs from the engine's ignition coil to a momentary switch mounted on the frame, creating a ground path when pressed to instantly cut power to the spark plug.
Safety was paramount in this design. The kill switch provides immediate engine shutdown capability, essential for emergency situations. The wiring is routed cleanly along the frame to prevent interference with moving parts while remaining easily accessible for quick activation.
- Gas Pedal Flow: Pedal → Steel Cable → Throttle Arm → Carburetor
- Kill Switch Flow: Ignition Coil → Wiring → Switch → Frame Ground
Quick Specs
- Engine: 212 cc (Predator class)
- Governor RPM: 3600 (stock)
- Gearing: 12T clutch → 60T axle (5:1)
- Tire OD: 13 in
- Mass (kart+driver): ~300 lb
Performance Math (How I Estimated Speed, Acceleration, and Braking)
I estimated performance using simple engineering relationships. To keep this page portable, I'm writing the math directly in HTML (no scripts or libraries).
1) Top Speed (mph)
The wheel speed comes from engine RPM divided by the gear ratio, and vehicle speed comes from wheel RPM times tire circumference:
Given:
engineRPM = e.g. 3600 (stock governor) or 5200 (modded)
gearRatio = axleTeeth / clutchTeeth (e.g. 60 / 12 = 5.00)
tireDiameter_in = outer tire diameter in inches (e.g. 13)
Tire circumference (in):
C_in = π × tireDiameter_in
Top speed (mph):
mph = (engineRPM / gearRatio) × (C_in) / 1056
Note:
1056 = (12 in/ft × 5280 ft/mi) / (60 min/hr)
Example: 3600 RPM, 5.00:1, 13" OD → mph ≈ 27.9
Raising RPM (removing governor) or using a taller gear ratio increases top speed.
2) 0–15 mph Estimate (Conceptual)
For a quick 0–15 mph estimate, I consider the smaller of two limits: (a) engine-limited tractive force at the tire, and (b) tire traction limit. In words:
Wheel radius (ft):
r = (tireDiameter_in / 12) / 2
Engine torque (flat estimate):
T_engine ≈ 8.1 ft·lb (stock 212 cc)
Wheel torque:
T_wheel = T_engine × gearRatio × drivetrainEfficiency
Engine-limited tractive force (lbf):
F_engine = T_wheel / r
Tire traction limit (lbf):
F_traction = μ_accel × (mass_lb) × (drivenNormalLoadFraction)
Use the smaller force:
F = min(F_engine, F_traction)
Convert mass to slugs:
m_slugs = mass_lb / g, with g = 32.174 ft/s²
Acceleration:
a = F / m_slugs (ft/s²)
Integrate speed until it reaches 15 mph (≈ 22 ft/s).
Typical defaults I used: mass ≈ 300 lb, μaccel ≈ 0.8, drivetrain efficiency ≈ 0.85, driven load ≈ 55%.
This isn't a full simulator—just a transparent way to show my assumptions and reasoning.
3) Braking Distance from 15 mph
Assuming tire-limited braking with a constant deceleration:
Given:
v₀ (ft/s) = 15 mph × 1.46667 ≈ 22.0 ft/s
a_brake = μ_brake × g, with g = 32.174 ft/s²
Distance (ft):
s = v₀² / (2 × a_brake)
Time to stop (s):
t = v₀ / a_brake
Typical μ_brake for sticky kart tires: 0.8–1.0
4) Turning Radius (If Steering Angle Known)
Using a simple bicycle model with wheelbase L and inside wheel steering angle θ:
R (ft) = (wheelbase_in / 12) / tan(θ)
Predicted vs. Measured
I used the math above to estimate performance, then compare it with my test results below.
| Metric | Predicted | Measured | Notes |
|---|---|---|---|
| Top speed (mph) | 44.7 | 45 | Phone GPS, straight run; rpm≈5200, 54/12 (4.5:1), 13" OD |
| 0–15 mph (s) | ~3.2 | 4.6 | mass ~300 lb, μaccel ≈ 0.8, η ≈ 0.85 |
| Braking 15→0 (ft) | ~8.5 | 6 | μbrake ≈ 0.9 (tire-limited) |
| Turning radius (ft) | ~7.5 | ~6.5 | wheelbase ~42", inside steer ≈25° (bicycle model) |
Problems and How I Overcame Them
- Chain Compatibility Crisis: The T8F chains required for the axle sprocket were completely unavailable, and the standard centrifugal clutch was incompatible. Solution: I innovated by bolting together a T8F sprocket with a 420 sprocket, creating a hybrid assembly that maintained proper chain engagement while enabling clutch compatibility.
- Material Failure Under Load: My initial 3D-printed steering components snapped catastrophically under the weight and forces of operation, creating a dangerous steering failure. Solution: I completely redesigned the system using steel square tubing, had it precision-cut to specifications, and welded it directly to the spindle mechanism for structural integrity.
- Brake System Degradation: The hydraulic brake system I initially installed lost stopping power over time due to fluid leaks and seal degradation, creating a critical safety hazard. Solution: I switched to a mechanical brake system that uses direct mechanical linkage, eliminating fluid dependency and providing consistent, reliable stopping power.
- Electrical System Confusion: The kill switch wiring was initially misconfigured, with incorrect grounding that prevented proper engine shutdown. Solution: I traced the ignition coil wire path, properly grounded the kill switch to the frame, and tested the circuit to ensure immediate engine cutoff capability.
- Steering Precision Issues: The rack-and-pinion steering system had excessive play and inconsistent response due to inadequate stabilization. Solution: I designed and 3D-printed a custom stabilizer component that eliminated unwanted movement while maintaining smooth steering operation.
- Frame Material Limitations: The wooden frame, while innovative, required reinforcement at stress points to handle the dynamic loads of operation. Solution: I strategically added steel reinforcement plates at critical joints and stress concentrations to maintain the wooden aesthetic while ensuring structural safety.
What I'd Build Next at Penn/MIT
Going forward, I'd love to join a hands-on team where I can iterate on real systems—combining lightweight materials, accessible manufacturing (CNC/CAD/3D printing), and test-driven engineering to push performance safely. I'm excited to contribute to projects that blend practical constraints with rigorous analysis, and to learn from peers and mentors who care about building things that actually work in the world.